1. Field of the Invention
The present invention relates to an image forming apparatus which has a heat member for heating a recording material bearing an unfixed image thereon and is configured so that a longitudinal center of the heat member becomes a conveyance center (the center with respect to the direction intersecting with a conveyance direction) of the recording material, that is, relates to an image forming apparatus of an electrophotographic system or the like, for transporting (paper feeding) a recording material by setting a center of the recording material to be transported as reference.
In addition, in this specification, even a plurality kinds of recording materials whose paper widths in a direction intersecting with the conveyance direction differ with each other, in the case of being set correctly, such a configuration that the width center of each recording material is transported at a certain position (generally, a longitudinal center position of the heat member) with respect to the direction intersecting with the conveyance direction is referred to as “a center of the paper feeding reference”, and its line is referred to as “a center line of the paper feeding reference”.
2. Related Background Art
It has been generally acknowledged that a conventional image forming apparatus of an electrophotographic system is a system which fixes a toner image on a recording material surface by being transported in sandwiched relation while being subject to a heat and a pressure simultaneously by using a heating device which is typified by a heat roller system using a halogen lamp, a film heating system using a ceramic heater, or the like as fixing means of the toner image on the recording material (recording paper).
In such a heating device, when a recording material having a narrow paper width such as a postcard and an envelope is continuously fed, there generates a non-paper feeding part temperature rise that gradually raises temperature at an area where the recording material is not passed. Therefore, as shown in, for example, Japanese Patent Application Laid-Open Nos. 03-18883 and 2001-282036, control that changes a control temperature of heating means and a conveyance time interval of the recording material is generally performed so that a temperature at an end portion, which is a non-paper feeding part of heating means, becomes not more than a predetermined temperature by equipping temperature detection part at an end portion in a longitudinal direction of the heating means in the heating device.
However, in the image forming apparatus using a center of the paper feeding reference which serves as reference for paper feeding of the recording material, there is a possible situation in which a small size recording material is not often set correctly in the center of the paper feeding reference due to miss handling in setting the recording material with respect to a paper feeding part. By this, there is a possibility that the small size recording material is fed and transported to inside the image forming apparatus like one side paper feeding reference conveyance in lateral deviation from a center of the paper feeding reference line. Therefore, end portion temperature detection part of heating means is covered within the paper feeding area, so that there is a possible situation that the non-paper feeding part temperature rise cannot be detected at all. Consequently, heating means part, which corresponds to a non-paper feeding area width appeared on the end portion side opposite to the side that the end portion temperature detection part is provided, is uncontrollably increased in temperature at the non-paper feeding part; thus, an excessively heated state may occur as the small size recording material is continuously fed and transported.
Further, since only one end portion temperature detection part is provided, more specifically, in an apparatus capable of feeding a recording material of not less than A3 size, it is difficult to accurately detect the highest temperature portion when the recording materials having various kinds of sizes including non-standard sizes are fed, and therefore, it cannot help degrading specification in consideration of safety.
In addition, inventions disclosed in Japanese Patent Laid-open Nos. 2002-296965 and 2003-15498 were made in order to solve such a problem, but further improvement is required.